1. Field of the Invention
This invention relates to an apparatus for applying a solution onto a substrate, and more particularly, to an apparatus for coating a layer of an ink solution onto the substrate for use in pre-press proofing.
2. Description of Related Art
Reproduction of color images through printing is an involved process requiring a breakdown of an original image into a number of fundamental single color images and the eventual recombination of the single color images through multiple printings into a full color reproduction of the original.
First color image reproduction typically includes the following steps using filtering and other photographic techniques a number of color separations are produced, typically four. Each separation bearing a halftone dot and/or a continuous tone image corresponding, for instance, magenta, cyan, yellow and black portions of the original. Second, a printing plate is made for each color separation by exposing a sensitized plate through one of the separations and developing the plate. Third, the printing plates are mounted on a multistage printing press which prints inks on a substrate, typically paper, sequentially and in register, one on top of another, four halftone and/or continuous tone images corresponding to each of the color separations to create a full color reproduction of the original.
It is desirable to be able to predict the final image appearance before it is printed, and preferably before making printing plates by reviewing images made directly from the color separations. The art of evaluating the color separations and deciding whether the various colors have indeed been properly separated is called proofing. Proofing is a process which uses the color separations to create a colored image called a proof to visualize what the final printed image will look like typically without actually making printing plates and running the printing press. Proofing through the creation of proofs shows the printer and customer what the job will look like after printing, so changes can be made, if necessary, to the color separations before the job goes to press where it can waste expensive press time, paper and ink if it is not right. Proofs are used for many purposes including for customer approval, for checking compatibility of a number of subjects to be printed on the same plate or job, for internal quality checking and control, and for relatively small numbers of final reproductions.
Although proofs can be made on special proof presses, generally proofs made by photochemical or photomechanical means have been preferred as a less expensive and faster alternative. These proofs are often referred to as offpress prepress or preplate proofs.
Photochemical or photomechanical proofing systems typically use photosensitive elements in making proofs. These systems generally make proofs by exposing photosensitive elements to actinic radiation through one of the image bearing separations to produce a duplicate image. This is either a positive or a negative of the separation depending on the element used. The radiation may make soluble areas insoluble, insoluble areas soluble, tacky areas nontacky, or nontacky areas tacky depending on the element used. After imagewise exposure, the photosensitive element can be developed by washing out soluble areas. Then tacky areas of the element may have to be toned with a dry or liquid colorant. This process is repeated for all color separations. Then the processed elements are laminated together one at a time sometimes on a support or a substrate. Protective layers may be peeled apart and removed from the elements before they are laminated to the support or other image elements. Finally the four color images may be transferred from the support to a receptor, transfer or display sheet such as a sheet of paper, to form the final proof.
There is a need to provide these conventional four color proofs with one or more additional custom colors to closely simulate the desired printed image. Custom colors are often added to printed images for advertising purposes to highlight particular parts of a printed image. However, due to the plethora of possible custom colors, mass production of photosensitive elements with each custom color is not cost effective.
Commercially available devices for coating a solution on a substrate generally includes an assembly having a meyer rod applicator. However, such devices produce a coating layer that is often defective because of non-uniformities such as density variations, streaks and other defects, which are unacceptable for proofing applications. In many cases the coating assembly requires manual operation where an operator positions and holds the meyer rod applicator: thus operator variability often causes the aforementioned defects. In addition, the size of the substrate which can be coated are often limited in many commercially available devices.